There are, at present, several different arrangements for electric space heating of residential and industrial environments. One widely-used electrical space heating method is direct resistance heating. In this type of system, heat is generated by running electric current through an electrical circuit which includes resistive wire coils. The electrical heating circuit is controlled by means of a thermostat which operates the heating coils in response to the demands of the heated environment.
Although simple in construction and operation, direct resistance heating has several associated drawbacks. One such drawback is that is places heavy demands on the electric power source. This problem occurs because the demand for both residential and industrial space heating is usually highest during the peak period of industrial demand. Therefore, power companies providing both industrial and residential heating power must provide for high peak capacities during the normal daytime hours. One direct result is that the total cost of producing the electricity is increased and, in particular, electrical use rates are highest during the space heating period causing the direct resistance heating system to be relatively expensive to operate.
In order to solve this problem and to provide a more balanced load for power and utility companies, electric storage heating is commonly used in many countries. In this type of heating heat is not provided directly to the heated environment from electrical resistance elements but instead resistive elements are used to heat a "storage" medium which usually consists of thermal brick or other material with a high heat capacity. The storage material is heated or "charged" during a time when electrical demands are low, usually at night. During the peak space heating hours (usually during the day when electrical demands are high) charging of the storage medium is discontinued and the heat is removed or "discharged" from the heat storage medium by circulating air over the storage medium with a fan. Such an arrangement allows electrical space heating to be performed at off-peak electrical rates, therefore, it is less expensive to operate. In addition, due to a reduced peak load on the utilities the electrical rate offered by the utilities is often considerably lower.
For multi-room residences and industrial applications, an electrical storage space heating system is usually designed with a set of remotely located heating units which are controlled from a central location in order to coordinate the operation of the heaters. With this arrangement, circuitry at the central location can economically control the charging time for the remote units. In addition, more sophisticated circuitry can be added which controls the charging of the remote heaters in relation to the outside ambient temperature. This latter arrangement allows the heating units to be operated with increased efficiency.
While electric storage heating has been an attractive alternative in new construction, it has found limited use for retrofitting of heating systems in existing buildings. This problem is due to the prior art control circuitry used to control the remote storage units from the central location. Typically, control signals generated at the central location are provided to the remote heaters by hard-wired control cables between the central control device and the remote storage units. Since such cables are not present in existing buildings with direct resistance heating, it has been considered uneconomical to rewire the buildings for electrical storage heating.
Therefore, it is an object of the present invention to provide an electrical heating control arrangement which allows a storage heating system to be easily retrofitted into existing buildings with direct electrical heating.
It is another object of the invention to provide an electrical storage heating control which is also economical when used in new construction.
It is a further object of the invention to eliminate the requirement for hard-wired control cables between the central location and the remote space heaters.
It is yet a further object of the invention to provide an electric storage space heater control which would allow a central control to control an unlimited number of electric storage heaters.
It is still another object of the invention to eliminate maintenance problems associated with hard-wired cable runs between the central location and remote space heaters.
It is yet another object of the invention to avoid switching high current heating element power at the central location.
It is a further object of the invention to provide an electric space heater control in which all heater control voltages originate at the remote location.